Assembly Of Arrays Research Articles

Performance Evaluation of a Modular Detector Unit for X-Ray Computed Tomography

A research prototype CT scanner is currently under development in our lab. One of the key components in this project is the CT detector. This paper describes the design and performance evaluation of the modular CT detector unit for our proposed scanner. It consists of a Photodiode Array Assembly which captures irradiating X-ray photons and converts the energy into electrical current, and a mini Data Acquisition System which performs current integration and converts the analog signal into digital samples. The detector unit can be easily tiled together to form a CT detector. Experiments were conducted to characterize the detector performance both at the single unit level and system level. The noise level, linearity and uniformity of the proposed detector unit were reported and initial imaging studies were also presented which demonstrated the potential application of the proposed detector unit in actual CT scanners.

Programmed self-assembly of DNA origami nanoblocks into anisotropic higher-order nanopatterns

Anisotropic nanopatterns have potentials in constructing novel plasmonic structures which have various applications in such as super-resolution microscopy, medicine, and sensors. However, it remains challenging to build big anisotropic nanopatterns that are suitable for big noble metal nanoparticles. Herein, we report a simple and reliable strategy for constructing DNA origami-based big anisotropic nanopatterns with controlled size and shape, nanoscale resolution, and fully addressability. Two kinds of basic DNA origami nanoblocks — cross-shaped and rectangular DNA origami units were used. We have demonstrated that by encoding nanoblocks’ edges, anisotropic higher-order nanopatterns, such as dimer, trimer, tetramer and mini “windmill” like pentamer nanopatterns could be constructed. To show the potential use as template to direct the assembly of anisotropic nanoparticles arrays, a proof of concept work was conducted by anchoring streptavidin nanoparticles on the “windmill” template to form a chiral array. Significantly, these nanopatterns have the sizes of hundreds of nanometers, which are in principle also suitable for big noble metal nanoparticles arrays.

Transcription activator‐like effector nucleases (TALENs): A highly efficient and versatile tool for genome editing

Transcription activator-like effector (TALE) nucleases (TALENs) have recently emerged as a revolutionary genome editing tool in many different organisms and cell types. The site-specific chromosomal double-strand breaks introduced by TALENs significantly increase the efficiency of genomic modification. The modular nature of the TALE central repeat domains enables researchers to tailor DNA recognition specificity with ease and target essentially any desired DNA sequence. Here, we comprehensively review the development of TALEN technology in terms of scaffold optimization, DNA recognition, and repeat array assembly. In addition, we provide some perspectives on the future development of this technology.

Grid Assembly-Free 60-GHz Antenna Module Embedded in FR-4 Transceiver Carrier Board

A novel antenna module solution which dramatically alleviates cost and fabrication related limitations of traditional 60-GHz antenna modules is demonstrated. The antenna topology is wholly devised using industry standard FR-4 PCB and is integrated into the 60-GHz transceiver carrier board. As a result, the proposed approach effectively bypasses the need for any complicated grid array assemblies for the first time to the author's best knowledge. The antenna element is first designed and confirmed to exhibit more than 9-GHz bandwidth and 71% average radiation efficiency from 57–66 GHz. The design is further expanded into an 8-element phased array module and integrated with a 60-GHz RFIC transceiver and digital interface. The overall footprint of the antenna module within the carrier board is 20 $\,\times\,$ 20 $\,\times\,$ 0.838 mm $^{3}$ . System-level evaluation confirms the 8-element phased array module to be highly sufficient in scan range, side lobe levels and radiation efficiency for 60-GHz wireless systems, particularly in the field of consumer electronics.

Innovative Mechanisms for Precision Assembly and Actuation of Arrays of Nanowire Oscillators

Bottom-up assembling of Micro/Nano Electromechanical System (MEMS/NEMS) devices from nanoscale building blocks is highly desirable but extremely difficult to achieve. In this work, we report innovative mechanisms for precision assembly and actuation of arrays of nanowire NEMS devices that can synchronously oscillate between two designated positions for over 4000 cycles. The assembly and actuation mechanisms are based on unique magnetic interactions between nanoentities with perpendicular magnetic anisotropy (PMA) and electric-tweezer manipulation, our recent invention. Quantitative analysis of the dynamics of torques involved in the nano-oscillators reveals that the induced electrostatic torques due to the external electric fields between metallic NEMS components play a significant role in the mechanical actuation. These new findings are expected to inspire new in situ assembly and actuation strategies in the general field of NEMS devices such as nanomechanical switches for toggling on/off circuits and nanoresonators for biochemical sensors and radio frequency communication.

Guiding Spatial Arrangements of Silver Nanoparticles by Optical Binding Interactions in Shaped Light Fields

We demonstrate assembly of spheroidal Ag nanoparticle clusters, chains and arrays induced by optical binding. Particles with diameters of 40 nm formed ordered clusters and chains in aqueous solution when illuminated by shaped optical fields with a wavelength of 800 nm; specifically, close-packed clusters were formed in cylindrically symmetric optical traps, and linear chains were formed in line traps. We developed a coupled-dipole model to calculate the optical forces between an arbitrary number of particles and successfully predicted the experimentally observed particle separations and arrangements as well as their dependence on the polarization of the incident light. This demonstrates that the interaction between these small Ag particles and light is well described by approximating the particles as point dipoles, showing that these experiments extend optical binding into the Rayleigh regime. For larger Ag nanoparticles, with diameters of approximately 100 nm, the optical-binding forces become comparable to the largest gradient forces in the optical trap, and the particles can arrange themselves into regular arrays or synthetic photonic lattices. Finally, we discuss the differences between our experimental observations and the point dipole theory and suggest factors that prevent the Ag nanoparticles from aggregating as expected from the theory.

Contact printing of horizontally-aligned p-type Zn3P2 nanowire arrays for rigid and flexible photodetectors

Zn3P2 is an important p-type semiconductor with the ability to detect almost all visible and ultraviolet light. By using the simple and efficient contact printing process, we reported the assembly of horizontally-aligned p-type Zn3P2 nanowire arrays to be used as building blocks for high performance photodetectors. Horizontally-aligned Zn3P2 nanowire arrays were first printed on silicon substrate to make thin-film transistors, exhibiting typical p-type transistor behavior with a high on/off ratio of 103. Besides, the Zn3P2 nanowire array based devices showed a substantial response to illuminated lights with a wide range of wavelengths and densities. Flexible photodetectors were also fabricated by contact printing of horizontally-aligned Zn3P2 nanowire arrays on flexible PET substrate, showing a comparable performance to the device on rigid silicon substrate.

ChemInform Abstract: 1,1′‐Bis(diphenylphosphino)ferrocene in Functional Molecular Materials

AbstractReview: 59 refs.

Arrays of single-walled carbon nanotubes with full surface coverage for high-performance electronics

Single-walled carbon nanotubes have exceptional electronic properties and have been proposed as a replacement for silicon in applications such as low-cost thin-film transistors and high-performance logic devices. However, practical devices will require dense, aligned arrays of electronically pure nanotubes to optimize performance, maximize device packing density and provide sufficient drive current (or power output) for each transistor. Here, we show that aligned arrays of semiconducting carbon nanotubes can be assembled using the Langmuir-Schaefer method. The arrays have a semiconducting nanotube purity of 99% and can fully cover a surface with a nanotube density of more than 500tubes/µm. The nanotube pitch is self-limited by the diameter of the nanotube plus the van der Waals separation, and the intrinsic mobility of the nanotubes is preserved after array assembly. Transistors fabricated using this approach exhibit significant device performance characteristics with a drive current density of more than 120µAµm(-1), transconductance greater than 40µSµm(-1) and on/off ratios of ∼1×10(3).

Cortical Microtubule Arrays Are Initiated from a Nonrandom Prepattern Driven by Atypical Microtubule Initiation

The ordered arrangement of cortical microtubules in growing plant cells is essential for anisotropic cell expansion and, hence, for plant morphogenesis. These arrays are dismantled when the microtubule cytoskeleton is rearranged during mitosis and reassembled following completion of cytokinesis. The reassembly of the cortical array has often been considered as initiating from a state of randomness, from which order arises at least partly through self-organizing mechanisms. However, some studies have shown evidence for ordering at early stages of array assembly. To investigate how cortical arrays are initiated in higher plant cells, we performed live-cell imaging studies of cortical array assembly in tobacco (Nicotiana tabacum) Bright Yellow-2 cells after cytokinesis and drug-induced disassembly. We found that cortical arrays in both cases did not initiate randomly but with a significant overrepresentation of microtubules at diagonal angles with respect to the cell axis, which coincides with the predominant orientation of the microtubules before their disappearance from the cell cortex in preprophase. In Arabidopsis (Arabidopsis thaliana) root cells, recovery from drug-induced disassembly was also nonrandom and correlated with the organization of the previous array, although no diagonal bias was observed in these cells. Surprisingly, during initiation, only about one-half of the new microtubules were nucleated from locations marked by green fluorescent protein-γ-tubulin complex protein2-tagged γ-nucleation complexes (γ-tubulin ring complex), therefore indicating that a large proportion of early polymers was initiated by a noncanonical mechanism not involving γ-tubulin ring complex. Simulation studies indicate that the high rate of noncanonical initiation of new microtubules has the potential to accelerate the rate of array repopulation.

Fabrication and assembly of ultrathin high-efficiency silicon solar microcells integrating electrical passivation and anti-reflection coatings

Intensive research into ultra-thin silicon solar cell applications has generated interesting approaches to reducing both critical materials usage and their associated device and module-level costs. Here we report an extension of previous work on micro-scale Si solar cells, devices fabricated using precise methods of micromachining Si(111) wafers in conjunction with wafer-scale processing. Here we describe a simple yet robust approach to fabricate the silicon microcells by re-designing the device structure, incorporating a thermally grown oxide layer to serve as a wet-etch and diffusion mask, and illustrate modes of light management and array assembly that can provide high-efficiency PV conversion of light to electrical energy. We report a best cell efficiency of 11.7% under an AM1.5D solar spectrum for an optically thin (30 µm thick) device, which is a substantial improvement over previously reported Si solar µ-cells. We show that the improvement attends to both the optimization made in the doping profiles of the device and the presence of the thermal oxide layer, which doubles as an effective electrical passivation and anti-reflection layer. External quantum efficiency measurements specifically show a marked improvement in the blue response that results from mitigating losses due to surface recombination in the high-surface-area, micro-scale devices. We highlight new strategies for integrating these devices into functional, interconnected arrays, using front and backside electrical bus contacts, with optimized spatial distributions on transparent glass substrates. This geometry, with optimized reflector and waveguiding planarization layers, creates a simple concentrator module by redirecting light via internal reflection to illuminate the sidewalls and bottom surfaces.

Dynamic templating: a large area processing route for the assembly of periodic arrays of sub-micrometer and nanoscale structures

A substrate-based templated assembly route has been devised which offers large-area, high-throughput capabilities for the fabrication of periodic arrays of sub-micrometer and nanometer-scale structures. The approach overcomes a significant technological barrier to the widespread use of substrate-based templated assembly by eliminating the need for periodic templates having nanoscale features. Instead, it relies upon the use of a dynamic template with dimensions that evolve in time from easily fabricated micrometer dimensions to those on the nanoscale as the assembly process proceeds. The dynamic template consists of a pedestal of a sacrificial material, typically antimony, upon which an ultrathin layer of a second material is deposited. When heated, antimony sublimation results in a continuous reduction in template size where the motion of the sublimation fronts direct the diffusion of atoms of the second material to a predetermined location. The route has broad applicability, having already produced periodic arrays of gold, silver, copper, platinum, nickel, cobalt, germanium and Au-Ag alloys on substrates as diverse as silicon, sapphire, silicon-carbide, graphene and glass. Requiring only modest levels of instrumentation, the process provides an enabling route for any reasonably equipped researcher to fabricate periodic arrays that would otherwise require advanced fabrication facilities.

Simulation Investigations on Fluid/Structure Interaction in the Reflow Soldering Process of Board-Level BGA Packaging

The objective of the present study is to develop a Fluid/Structure Interaction model of a board-level Ball Grid Array (BGA) assembly for an infrared-convection reflow oven. The infrared-convection reflow oven is modeled in Computational Fluid Dynamic (CFD) software while the structural heating BGA package simulation is done using Finite Element Method (FEM) software. Both software applications are coupled bidirectional using the Multi-physics Code Coupling Interface (MpCCI). The simulation thermal profile is compared with the experiment thermal profile, and they were found to be in good conformity. The simulated flow fields show that the convection mode in an infrared-convection reflow oven played minor effect on heat transfer to the printed circuit board (PCB). The dominant heat transfer mode in an infrared-convection reflow oven is the radiation mode from a quartz heating tube. From the simulation results, the PCB near the edges or corners tended to heat up first at preheating, soaking and reflow stages. The PCB and component experience larges temperature difference in preheating stage. This situation runs the risk of an excessive board warpage. In addition, the maximum von-Mises stress is trapped in the interfaces between solder joint and die, which intend to form the nucleation of initial solder joint crack. This guideline is very useful for the accurate control of temperature and thermal stress distributions within components and PCB, which is one of major requirements to achieve high reliability of electronic assemblies.

Self-Assembly of Segmented Anisotropic Particles: Tuning Compositional Anisotropy To Form Vertical or Horizontal Arrays

Columnar arrays of anisotropic nano- and microparticles, in which the long axes of the particles are oriented perpendicular to the substrate, are of interest for photovoltaics and other applications. Array assembly typically requires applied electric or magnetic fields and/or controlled drying, which are challenging over large areas. Here, we describe a scalable approach to self-assemble multicomponent nanowires into columnar arrays. Self-assembly of partially etched nanowires (PENs) occurred spontaneously during sedimentation from suspension, without drying or applied fields. PENs, which have segments that are either gold or "empty" (solvent-filled) surrounded by a silica shell, were produced from striped metal nanowires by first coating with silica and then removing sacrificial segments by acid etching. Electrostatic repulsion between the particles was necessary for array assembly; however, details of PEN surface chemistry were relatively unimportant. The aspect ratio and relative center of mass (COM) of the PENs were important for determining whether the PEN long axes were vertically or horizontally aligned with respect to the underlying substrate. Arrays with predominantly vertically aligned particles were achieved for PENs with a large offset in COM relative to the geometric center, while other types of PENs formed horizontal arrays. Assemblies were formed over >10 cm(2) areas, with over 60% of particles standing. We assessed array uniformity and reproducibility by imaging many positions within each sample and performing multiple assemblies of differently segmented PENs. This work demonstrates the versatility of gravity-driven PEN array assembly and provides a framework for designing other anisotropic particle systems that self-assemble into columnar arrays.

A ligation-independent cloning technique for high-throughput assembly of transcription activator–like effector genes

Transcription activator–like (TAL) effector proteins derived from Xanthomonas species have emerged as versatile scaffolds for engineering DNA-binding proteins of user-defined specificity and functionality. Here we describe a rapid, simple, ligation-independent cloning (LIC) technique for synthesis of TAL effector genes. Our approach is based on a library of DNA constructs encoding individual TAL effector repeat unit combinations that can be processed to contain long, unique single-stranded DNA overhangs suitable for LIC. Assembly of TAL effector arrays requires only the combinatorial mixing of fluids and has exceptional fidelity. TAL effector nucleases (TALENs) produced by this method had high genome-editing activity at endogenous loci in HEK 293T cells (64% were active). To maximize throughput, we generated a comprehensive 5-mer TAL effector repeat unit fragment library that allows automated assembly of >600 TALEN genes in a single day. Given its simplicity, throughput and fidelity, LIC assembly will permit the generation of TAL effector gene libraries for large-scale functional genomics studies.

Topographically induced hierarchical assembly and geometrical transformation of focal conic domain arrays in smectic liquid crystals

Controlling topological defects in 3D liquid crystal phases is a crucial element in the development of novel devices, from blue-phase displays to passive biochemical sensors. However, it remains challenging to realize the 3D topological conditions necessary to robustly and arbitrarily direct the formation of defects. Here, using a series of short pillar arrays as topological templates, we demonstrate the hierarchical assembly of focal conic domains (FCDs) in smectic-A liquid crystals that break the underlying symmetry of the pillar lattice, exhibit tunable eccentricity, and together develop a nontrivial yet organized array of defects. The key to our approach lies in the selection of the appropriate ratio of the size of focal domain to the dimension of pillars such that the system favors the "pinning" of FCD centers near pillar edges while avoiding the opposing effect of confinement. Our study unequivocally shows that the arrangement of FCDs is strongly influenced by the height and shape of the pillars, a feature that promotes both a variety of nontrivial self-assembled lattice types and the attraction of FCD centers to pillar edges, especially at regions of high curvature. Finally, we propose a geometric model to reconstruct the smectic layer structure in the gaps between neighboring FCDs to estimate the energetic effects of nonzero eccentricity and assess their thermodynamic stability.

Decorrelated Feature Space and Neural Nets Based Framework for Failure Modes Clustering in Electronics Subjected to Mechanical Shock

Electronic systems under extreme shock and vibration environments may sustain several failure modes simultaneously. Previous experience indicates that the dominant failure modes experienced by packages in a drop and shock framework are in the solder interconnects including cracks at the package and the board interface, pad cratering, copper trace fatigue, and bulk-failure in the solder joint. In this paper, a method has been presented for failure mode classification using a combination of Karhunen Loeve transform with parity-based stepwise supervised training of a perceptrons. New is the early classification of multiple failure modes in the pre-failure space using supervised neural networks in conjunction with a Karhunen Loeve transform. The feature space has been formed by joint time frequency analysis. Because the cumulative damage may be accrued under repetitive loading with exposure to multiple shock events, the area array assemblies have been exposed to shock and feature vectors constructed to track damage initiation and progression. The error back propagation learning algorithm has been used for stepwise parity of each particular failure mode. The classified failure modes and failure regions belonging to each particular failure mode in the feature space are also validated by simulation of the designed neural network used for parity of feature space. Statistical similarity and validation of different classified dominant failure modes is performed by multivariate analysis of variance and Hotelling's T-square. The results of different classified dominant failure modes are also correlated with the experimental cross sections of the failed test assemblies. The methodology adopted in this paper can perform real-time fault monitoring with identification of a specific dominant failure mode, and is scalable to system level reliability.

Laser surface micro-/nano-structuring by a simple transportable micro-sphere lens array

A micro-sphere array optic was employed for laser surface micro-structuring. This array optic consists of a hexagonally close-packed monolayer of silica micro-spheres. It was organized through a self-assembly process and held together on a glass support, without using any adhesives. The array assembly was then reversed, placed in direct contact with the substrate and exposed to 515 nm, 6.7 ps laser pulses. During the exposure, the silica spheres act as micro-lenses, which enhance the near-field light intensity underneath them. As the spheres are confined in the space between the substrate and glass support, they are not ejected during laser machining. Using this type of direct write laser machining, a large number of identical features (nano-holes) can be produced in parallel simultaneously. The holes drilled are a few hundred nanometres in diameter and the depth depends on the number of laser pulses applied. The impact of laser machining on the micro-spheres was also studied. The micro-spheres were contaminated or partially damaged after micro-structuring. Combination of a moderate laser pulse energy and multiple shots was found to ensure a good surface structuring quality and minimum damage to the spherical particles.

Focus on materials

Focus on materials

Photochemical Assembly of Gold Nanoparticle Arrays Covalently Attached to Silicon Surface Assisted by Localized Plasmon in the Nanoparticles

It is essential to immobilize gold nanoparticles (AuNPs) firmly onto a certain substrate in a closely packed manner to apply plasmonic functions of AuNP in photonic/electronic devices. AuNP-Si systems are of particular interest for the integration of plasmonics to semiconductor electronics. Here we report on the arrangement of AuNPs into a 2-D array that was covalently bonded to a Si substrate without surface oxide. This process was achieved by simply irradiating visible light to a hydogen-terminated Si substrate immersed in a solution of AuNPs covered with a self-assembled monolayer (SAM) of 11-mercaptoundecene (MUD). These MUD-AuNPs were attached to the substrate by forming Si–C bonds as a result of the photochemical reaction between Si–H groups on the substrate and vinyl groups of the MUD-SAMs. The reaction proceeded most effectively at a wavelength band around 520 nm adjusted to the plasmonic resonance peak of the MUD-AuNPs(20 nm in diameter)/toluene solution centered at 535 nm, demonstrating that the photochemical reaction was assisted by localized surface plasmon, which allowed the AuNPs to be photon collectors.